As one of capacitors having high capacity to be used for various electronic devices, there is given a solid electrolytic capacitor chip in which a solid electrolytic capacitor element comprises a dielectric oxide film, a semiconductor layer, and an electrode layer laminated sequentially on a rectangular parallelepiped sintered body of conductive powder having an anode lead planted on one surface thereof, and the solid electrolytic capacitor element is sealed with an exterior resin.
The solid electrolytic capacitor is manufactured by sealing a solid electrolytic capacitor element with a molding resin, the solid electrolytic capacitor element being composed of a sintered body (conductor) of conductive powder such as tantalum having fine pores, which serves as one electrode (anode), a dielectric layer formed on a surface layer of the electrode, the other electrode (in general, a cathode formed of a semiconductor layer) formed on the dielectric layer, and an electrode layer laminated on the other electrode. In a conductor of the same volume, the surface area in the conductor increases as each pore becomes smaller and the amount of pores becomes larger, and hence the capacity of a capacitor manufactured from the conductor becomes larger. In general, a sintered body having a high CV and a large volume has fine pores that have a long depth, and thus has a low filling rate of a semiconductor layer. The sintered body having a large number of pores not filled with a semiconductor has low strength, and a dielectric film thereof is easily degraded due to a stress. In particular, there is a problem in that the yield of the manufactured solid electrolytic capacitor degrades due to an increase in leakage current when the injection stress of resin displaces a solid electrolytic capacitor element from a position on a lead frame at which the solid electrolytic capacitor element has been mounted (horizontal abnormality), or an outer appearance defect occurs in such a way that minute holes (pin holes) not filled with resin are formed in a resin exterior body of a manufactured solid electrolytic capacitor.
The solid electrolytic capacitor element is sealed with resin through use of a transfer machine, for example, by disposing a lead frame having the solid electrolytic capacitor element mounted thereon in a mold and injecting resin from a resin injection port of the mold.
As a method of manufacturing a capacitor by transfer molding, JP 3071115 B2 (Patent Document 1), there is discloses a method involving mounting a buffer (such as synthetic resin, rubber and paper) onto a surface of a capacitor element facing a gate of a mold so as to diminish the injection pressure of an injection resin for molding. JP 04-357813 A (Patent Literature 2) discloses a method of reducing the leakage-current percent defective by providing a protective resin to a washer for preventing creep-up of a solid electrolyte on a side of the washer which faces a gate port of a mold, when a capacitor element having the washer is sealed with resin. Note that, none of these methods focuses on the arrangement of a mold gate (resin injection port) through which resin is injected at the time of sealing the capacitor element with resin through use of a transfer machine.
JP 2007-36092 A (Patent Document 3) discloses a method of providing a resin injection port of a mold at such a position that resin immediately after being injected (in an initial stage) is not brought into contact with a capacitor element (for example, in a gap between a cathode frame and an anode frame facing each other under an anode lead wire). However, in recent years, the dimensions of a sintered body have increased along with an increase in capacity of a capacitor, and hence the gap between the cathode frame and the anode frame becomes smaller than the injection port, which makes it difficult to locate the injection port at this position.
As an example, in a solid electrolytic capacitor chip having outer dimensions of 7.3×4.3×1.9 mm, the gap between a cathode frame and an anode frame is intended to fall within 1.0 mm. However, considering the flowability of an exterior resin and the outer diameter (generally, from about 0.01 to 0.09 mm) of a filler mixed in the resin, it is preferred that an injection port have dimensions of 1.2×0.1 mm or more, and thus it is difficult to locate the injection port at that position. Consequently, there is no choice but to locate the injection port at such a position that the exterior resin is brought into contact with a capacitor element during injection. In this case, there has been a problem that defective products are generated in which pin holes (minute holes not filled with the resin) are present in an exterior body after sealing with the resin, and an LC value is also out of a prescribed value.